1. Field of the Invention
This invention relates generally to cyclinder locks, and more specifically to a rekeyable lock method and apparatus that wherein a master key lock system can be rekeyed externally for different master level keys as well as for different user level keys.
2. Description of the Prior Art
Lock devices generally known as tumbler pin cylinder locks have been widely used for many years to secure door locks, padlocks, and many other types of locks. More recently, variations and improvements have been developed for rekeying such tumbler pin cylinder locks without having to disassemble the locks. The following U.S. patents are examples of such externally rekeyable or changeable combination locks: U.S. Pat. No. 3,078,705, issueed to D. Morrison, Jr.; U.S. Pat. No. 3,070,987, issued to A. R. Baker, et al; U.S. Pat. No. 3,125,878, issued to L. Gutman; U.S. Pat. No. 3,563,071, issued to L. N. Barger; U.S. Pat. No. 3,175,378, issued to F. J. Russell; U.S. Pat. No. 3,073,146, issued to G. P. Patriquin; and U.S. Pat. No. 1,650,568, issued to N. B. Hurd.
The Morrison patent, U.S. Pat. No. 3,078,705, as well as the Republic of Germany Patent No. DE 3040646AL, issued to F. Muus on June 19, 1981, disclose a method and apparatus for rekeying tumbler pin cylinder locks by utilizing a short temporary pin or wafer between the driver and tumbler pins to create a different shear line that is alignable by the appropriate key bitting with the shear line between the lock cylinder and housing to allow the cylinder to be rotated by the key. When the lock is to be rekyed, a special disabling key is inserted into the keyway in the cylinder. This special disabling key and bitting thereon cut to push the wafer into the top chamber and a notch in its spine opposite the bitting to receive and capture the wafer when the key and cylinder are rotated 180 degrees. The captured wafer is then extracted and expelled from the lock when the special key is pulled out of the keyway.
While the Morrison and Muus devices are effective to rekey the lock, there are several problems with its use. One of the most significant of these problems is that once the temporary pin or wafer is removed from the lock as taught by Morrison and Muus, one dare not reinsert the special disabling key into the keyway and turn the cylinder with it. If this is done, the top or driver pin in the top chamber will fall into the notch in the spine of the special disabling key. In that position, the cylinder cannot be turned again, and the special disabling key cannot be withdrawn. It remains stuck in that position, and the lock is rendered useless. It is, for practical purposes, ruined.
The only way to prevent this situation from occurring is to either destroy the special disabling key after its first use or take other elaborate precautionary measures to insure that it is not again mistakenly used in the lock. Unfortunately, many lock users do not take these precautions.
My improved rekeyable lock invention, on which my U.S. Pat. No. 4,412,437 was issued on Nov. 3, 1983, was an attempt to solve this problem. It utilizes a short temporary pin or wafer that is smaller in diameter than the main driver and tumbler pins in the lock. It also utilizes a notch in the spine of the special disabling or change key that is sized to capture the smaller diameter wafer, but which in combination with the keyway is too small to receive the larger diameter driver or top pin. Thus, the larger driver pin is physically prevented from entering the notch in the disabling or change key, even if that same disabling or change key is inserted into the keyway and turned after the wafer has been removed. While this improvement has eliminated the problem of irretrievably sticking the special disabling or change key in the lock, it does still have some unique problems of its own. The most significant of such problems is that the smaller diameter wafers have a tendency to flip over on their sides in the chamber, thus affecting the proper functioning of the lock.
The Morrison and Muus patents also are used only as construction keys wherein one key change is taught. My improved rekeyable lock invention in my issued U.S. Pat. No. 4,412,437 expands such usage to include several levels of key changes for users. However, all such prior art patents have been limited to apparatus in which either user levels or master levels could be changed but not both.
More specifically, a master key lock system is one in which a master key can be used to unlock all of a whole group of locks, each of which requires a different user key. Such systems are often used by building owners to give the owner, maintenance, or security people ready access to many premises in the building, while the tenant's or user's key can only provide access to a specific one of such premises. The purpose of the master key is to reduce the number of keys the owner, maintenance, or security people must carry or maintain. However, while such master key systems increase efficiency, the existence of the master keys also reduce security. If a master key is lost, stolen, or secretly copied, every tenant's or user's premises is more susceptible to unauthorized entry. If security is to be maintained, the owner must change all of the locks in the group for which the master key is operable. Such changing of many locks was a costly procedure prior to this invention, so there was often the temptation to forego this expense and hope for the best. Unfortunately, from this approach, losses could occur, and the owner could incur substantial legal liabilities. Therefore, it has been found desirable to be able to provide high security rekeyable locks in which both user level keying combination and master level keying combinations can be changed independently of each other and without affecting the operation or keying of the other.
Another fact that exacerbates the security problems with master key systems, as well as with rekeyable locks, is that these master and rekeying functions operate off a plurality of different shear planes between the driver and service pins of the lock. Unfortunately, the more shear planes, the easier it is to "pick" the lock and gain unauthorized entry. A number of improvements over the prior art are required to provide a lock system that is rekeyable for both the user and the master levels and is easy enough to use for ordinary individuals, yet reliable and secure enough to provide the protection for which locks are used.
Another limitation of the prior art rekeyable locks, such as the Morrison and Muus patents, as well as my prior art apparatus in my U.S. Pat. No. 4,412,437, is that the cylinders and keys in those locks have to be rotated 180 degrees in order to align the removal notch in the key spine with the temporary pin or wafer in order to capture and remove the wafer from the lock. Unfortunately, the latch mechanisms to which many of these locks are connected in doors, padlocks, and other devices, do not accomodate or allow 180 degress rotation of the lock cylinder. Such installations cannot utilize the rekeyable locks shown in the Morrison or Muus patents or in that rekeyable lock shown in my U.S. Pat. No. 4,412,437. Several other prior art patents, such as those issued to Patriquin, Russell, Baer, Barger, and Hurd, dislcose externally rekeyable locks that do not require 180 degree rotation of the cylinder, but they only show one available rekeying operation. Therefore, there is still a need for a rekayble lock that can be rekeyed a multiple of times externally for use with multiple user level and/or master level rekeying.
In summary, the prior art rekeyable locks do not provide multiple user level and master level rekeyable options. Further, they do not provide fool-proof mechanisms for users or sufficient security from being picked or opened by unauthorized persons, especially in the multiple level rekeyable configurations.
To further achieve the foregoing and other objects in accordance with the purpose of this invention as well as to facilitate practice of this invention, this invention also includes methods of assembling and using the lock apparatus summerized above for rekeying operations and increasing security of such lock.